The advantages of using liquid cooling of gas turbine buckets and nozzles are well known. Structural arrangements for open-circuit liquid cooling of gas turbine vanes are shown by Kydd U.S. Pat. No. 3,446,481. Further improvements were invented by Anderson, U.S. Pat. No. 4,156,582 which discloses water cooled turbine buckets wherein the water cooling channels are formed using preformed tubes which are located beneath an outer protective layer composed of an inner skin to provide high thermal conductivity and an outer skin to provide protection from hot corrosion.
Schilling et al, in U.S. Pat. application Ser. No. 924,981, filed July 17, 1978, now U.S. Pat. No. 4,183,456, discloses a method of fabricating cooled gas turbine buckets and nozzles which utilizes hot isostatic pressure with molten glass as a pressure transmitting medium. Preformed tubing is brazed into channels in the airfoil or core. Then the tubing and cladding are bonded to a core under conditions such that the ends of the tubing extend above the molten glass to prevent collapsing of the tubing during hot isostatic pressing.
A method of diffusion bonding to a convex-concave substrate is disclosed by Schilling et al, U.S. Pat. No. 3,952,939. According to this process, an oxidation and hot corrosion resistant cladding is metallurgically bonded by hot gas isostatic pressure to a structural alloy having a convex-concave surface, such as an air-foil employed in a nozzle or blade in a gas turbine.
Another method for fabricating complex composite components for water-cooled, high temperature gas turbines is disclosed by Beltran, et al, U.S. Pat. No. 4,137,619. Each component comprises a core, a thermally conducting layer of copper bonded to the core, metal tubing through which water may pass embedded in the layer, and a corrosion resistant cladding. The method utilizes powder metallurgy techniques to form the thermally conducting layer and hot isostatic pressure to bond the corrosion resistant cladding to the outer surface of said layer. While the process results in a usable component, it possesses several drawbacks. One of these is that the airfoil requires extensive and difficult machining to its final shape and dimensions. Another disadvantage is that welding of cladding pieces to each other, while in place over the heat conducting layer, can lead to poor quality welds at the joints.